We got an aquarium at the August Bank Holiday - Saturday was the trip where we chose the tank and listened to a knowledgeable, patient, enthusiastic and child-friendly member of staff at the Goldfish Bowl as he helped us through all the choices to be made and told us how to set it all up. On Bank Holiday Monday we were back to buy the fish themselves (you have to leave the initial water to settle for 48 hours or so) and since then we've been back once more to buy extras like a couple of water plants (additional to the plastic coral and plant-substitutes we bought on the first visit) and a hatchery plus baby food. Yes, we were told that the fish we chose (black and white spotted Mollys) are live-bearers, and it was only 10 days or so after we bought them that we spotted the first little tiny small fry darting around!
The internet had told me that fry are liable to get eaten by the grownup fish and I did warn the kids not to get too attached to the first one, just in case - and then we didn't see it except for sporadically over the next few days. I think maybe that first one perhaps did survive after all, but at any rate we now have 4 grown Mollys (3 females, 1 male), 5 babies in the hatchery where the adults can't snaffle them, and two hardy-seeming small fish darting around in the main tank doing good hiding and dodging. It's all rather cool (if a bit pricey every time you need to pop back to the shop for a bit more equipment or specialist food).
The grown ups are already named - Marina (Kid A's name choice - the silvery one), Judy (my choice, one out of the many girls comics names I could have used), Goldie (R's choice, in a nod to Peppa Pig's goldfish and Data's choice of an inappropriately-named pet), and Tunip Mikey (Kid B's choice in a mash up between one of the characters from Octonauts and Michelangelo from Teenage Mutant Ninja Turtles). We will have to see how many of the babies we keep and therefore name, and how many we take back to the fish shop as is apparently something people do.